We have studied by kinetic Chl-fluorescence imaging (Chl-FI) Nicotiana benthamiana plants infected with the Italian strain of the pepper mild mottle tobamovirus (PMMoV-I). We have mapped leaf photosynthesis at different points of the fluorescence induction curve as well as at different post-infection times. Images of different fluorescence parameters were obtained to investigate which one could discriminate control from infected leaves in the absence of symptoms. The non-photochemical quenching (NPQ) of excess energy in photosystem II (PSII) seems to be the most adequate chlorophyll fluorescence parameter to assess the effect of tobamoviral infection on the chloroplast. Non-symptomatic mature leaves from inoculated plants displayed a very characteristic time-varying NPQ pattern. In addition, a correlation between NPQ amplification and virus localization by tissue-print was found, suggesting that an increase in the local NPQ values is associated with the areas invaded by the pathogen. Changes in chloroplast ultrastructure in non-symptomatic leaf areas showing different NPQ levels were also investigated. A gradient of ultrastructural modifications was observed among the different areas.

of in vivo copper treatment on the photosynthetic apparatus of two Triticum durum cultivars with different stress sensitivity. -Physiol. Plant. 100: 901-908.The effect of copper on the photosynthetic apparatus of two cultivars of durum wheat (Triticum durum cvs Adamello and Ofanto) with different sensitivity to drought and nickel stress were investigated. Plants were grown in nutrient solution or in nutrient solution further supplemented with CUSO4 to achieve final concentrations of 3.6 [lM and 20 [xM Cu. Several fluorescence analyses were performed, in presence or absence of DCMU, and with varying light intensities. Furthermore, light and electron microscopic investigations were carried out. In vivo treatment using 3.6 |jA/ Cu produced a marked reduction in growth of the Cu-treated plants, but only mild effects on the fluorescence-related parameters. The Cu-induced reduction in the area above the fluorescence induction curve and in the time needed to reach the maximum of chlorophyll fluorescence (F^^J were more pronounced. These results favour the hypothesis that under such conditions copper affects photosynthesis mainly in an indirect way, causing a slowing down of the electron transport as a consequence of the reduced requirement for photosynthesis products. The morphological analyses corroborate this hypothesis, showing toxic effects on the chloroplast structure due to Cu treatment. The differences between the two cultivars were not as pronounced as reported in the case of nickel or drought stresses; nevertheless, cv. Ofanto seemed to be less sensitive also to Cu stress than cv. Adamello,

The effect of copper on the photosynthetic apparatus of two cultivars of durum wheat (Triticum durum cvs Adamello and Ofanto) with different sensitivity to drought and nickel stress were investigated. Plants were grown in nutrient solution or in nutrient solution further supplemented with CuSO4 to achieve final concentrations of 3.6 μM and 20 μM Cu. Several fluorescence analyses were performed, in presence or absence of DCMU, and with varying light intensities. Furthermore, light and electron microscopic investigations were carried out. In vivo treatment using 3.6 μ Cu produced a marked reduction in growth of the Cu‐treated plants, but only mild effects on the fluorescence‐related parameters. The Cu‐induced reduction in the area above the fluorescence induction curve and in the time needed to reach the maximum of chlorophyll fluorescence (Fmax) were more pronounced. These results favour the hypothesis that under such conditions copper affects photosynthesis mainly in an indirect way, causing a slowing down of the electron transport as a consequence of the reduced requirement for photosynthesis products. The morphological analyses corroborate this hypothesis, showing toxic effects on the chloroplast structure due to Cu treatment. The differences between the two cultivars were not as pronounced as reported in the case of nickel or drought stresses; nevertheless, cv. Ofanto seemed to be less sensitive also to Cu stress than cv. Adamello.

The effects of nickel (Ni) on growth, leaf water status, and mineral nutrient concentration were studied in two wheat (Triticum durum Desf.) cultivars with different sensitivity to water stress: 'Adamello' [drought sensitive (DS)] and 'Ofanto' [drought tolerant, (DT)]. The DT cultivar showed a higher Ni absorption capacity: 'Ofanto' seedlings grown in the presence of 35 ΜM Ni had a 3.5 times greater concentration of Ni in roots than did 'Adamello'. Despite the greater Ni tissue content, the DT cultivar exhibited better growth and nutritional status when compared to the DS cultivar. In the DS cultivar the concentration of chlorophyll a and b was reduced by Ni treatment. Chlorophyll a concentration decreased in the DT cultivar, but to a lesser extent than in the DS cultivar; chlorophyll b was not altered by Ni level in the DT cultivar. Nickel caused a decrease in the water potential (ψ w ) and relative water content (RWC) in both cultivars, but these decreases were greater in the DS cultivar. The antioxidative defense enzymes, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase, showed increased activity in Ni-treated DS seedlings; this increase in activity was not observed in the DT seedlings. These data suggest that different wheat genotypes may markedly differ in Ni uptake and sensitivity and that a enhanced capacity to counteract Ni stress may be associated with drought resistance.

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Chlorophyll fluorescence has been widely applied as a non-invasive technique for the in vivo analysis of plant stress. In this work, the two-dimensional image analysis of the fluorescence signal was used to evaluate the physiological status of heavy metal stressed leaves, based on their photosynthetic capacity. Chlorophyll fluorescence (>650nm) emission of control and heavy metal treated plants registered at different times during the blue light illumination of the leaves show abnormal patterns of non-homogeneous spatial distribution of the fluorescence emission from metal-treated plants. This is correlated to an altered photosynthetic functionality in different parts of the leaves. Quantitative evaluation of the photosynthetic activity can be made on data extracted after simple arithmetical pixel-point processing of fluorescence images taken at different time during the illumination process. The altered fluorescence emission was observed in absence of other visual symptoms that could testify problems at the level of the photosynthetic apparatus. This indicates that chlorophyll fluorescence imaging is a suitable tool for the early, pre-visual detection of plant stress also in the case of heavy metal stress.

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